The code designation of the lens is RT:C (R--refracting section (face) of a lens, T--transmitting section of a lens, and C--concentrating lens).
Prior art includes the following patents:
1. Biconical Refractor, U.S. Pat. No. 2,881,654, Apr. 14, 1959, D. S. Toffolo. This is a beam concentrator with an upper component lens which receives an annular incipient beam.
2. Conical Refractor, U.S. Pat. No. 2,882,784, Apr. 21, 1959, D. S. Toffolo. This is a beam concentrator with a convex conical section which is parallel to a concave conical section.
3. Reflective Beam Concentrator, U.S. Pat. No. 4,325,612, Apr. 20, 1982, John E. Clegg. This concentrator has a lens with a convex conical section which receives a convergent conical beam and with a concave conical section which emits a concentrated whole beam.